Casting, machining, and assembling a magnetic motor ring structure



Feb. 13, 1968 R. F. EBERLINE ET AL 3,368,275

CASTING, MACHINING, AND ASSEMBLING, A MAGNETIC MOTOR RING STRUCTURE Filed July 5, 1962 2 SheetsSheet 1 &

Feb. 13, 1968 R. F. EBERLINE ET AL 3,368,275

CASTING, MACHINING, AND ASSEMBLING, A MAGNETIC MOTOR RING STRUCTURE Filed July 3, 1962 2 Sheets-Sheet 2 3,368,275 CASTING, MACHINING, AND ASSEMBLIN-G A MAGNETIC MOTGR RING STRUCTURE Richard F. Eberline, Rochester, and Thomas F. Carmichael and Edward A. Schilling, Drayton Plains,

Micln, assignors to Syncro Corporation, Oxford,

Mich., a corporation of Michigan Filed July 3, 1962, Ser. No. 207,264 2 Claims. (Cl. 29-598) This invention relates to generators, and more particularly to a method and construction for permanent magnet alternators of the type having an outside rotor ring carrying circumferentially spaced permanent magnets of the ceramic type.

The use of ceramic type permanent magnets for the outside rotors of permanent magnet alternators has certain advantages, among which is the fact that a predetermined amount of induction can be obtained with ceramic magnets which are shorter in a radial direction as compared with Alnico magnets. However, in order to achieve the desired flux concentration, metallic shoes are placed on the inner surfaces of the ceramic magnets facing the stator.

It is an object of the present invention to provide a novel and improved method of construction for permanent magnet alternator rotors in which ceramic magnets and their associated metallic shoes will be rigidly secured in a unitary arrangement, facilitating their assembly in an outer support, such as a flywheel or ring gear unit.

Other objects, features, .and advantages of the present invention will become apparent from the subsequent description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a partly sectioned plan view of the magnet and shoe assembly after casting and machining but before it is placed in a ring support;

FIGURE 2 is a cross-sectional view taken along the line 22 of FIGURE 1 and showing the assembly mounted in a support ring;

FIGURE 3 is a cross-sectional view taken along the line 3-3 of FIGURE 1 and showing the shape of the casting between magnets;

FIGURE 4 is a partial cross-sectional view in elevation of a suitable die assembly for molding the magnet-supporting casting, showing the magnets and shoes in position;

FIGURE 5 is a fragmentary plan view of the lower die member, showing magnet-supporting and positioning elements;

FIGURE 6 is a front view of one of the magnet shoes;

FIGURE 7 is a front view of a modified form of magnet shoe in which edge portions are crimped around the ceramic magnet; and

9 FIGURE 8 is a cross-sectional fragmentary view taken along the line 8-8"of FIGURE 7 and showing the mannet in which the shoe portions engage the magnet.

Briefly, the illustrated embodiment of the invention comprises a plurality of circumferentially spaced curved ceramic magnets, each having a relatively thin metallic shoe engaging its concave surface, with a cast ring of nonmagnetic material engaging and partially surrounding the magnets, the ring serving to support the magnets and shoes and permitting them to be assembled as a unit into a supporting ring of magnetic material which engages the magnets. As a suitable process for making the magnet and shoe' assembly, a multiple member die or mold is provided, the magnets being positioned together with the shoes within the die while in a magnetized condition, the die members being provided with locating and supporting elements for the magnets and shoes. After the casting 'is formed the magnets are demagnetized, after which the unitary magnet and shoe assembly is placed in the supporting ring, the ring being previously heated so that it will shrink into tight engagement with the assembly. The cast ring is then machined at room temperature to remove its interior sufiiciently to expose the magnet shoes, and the magnets are then remagnetized.

Referring more particularly to the drawings, FIGURES 1, 2 and 3 show the magnet and shoe assembly which is generally indicated at 11 and is intended to be mounted in a supporting ring of magnetic material generally indicated at 12 and shown partially in dot-dash lines in FIG- URES 2 and 3. In its finished form, assembly 11 comprises a plurality of circumferentially spaced ceramic magnets 13 which may be fabricated by any of several known methods. Each magnet 13 has a concave inner surface 14 and a convex outer surface 15, these surfaces being concentric and being connected by parallel sides 16. Each magnet is provided with a shoe 17 of magnetic material, the width and length of this shoe being substantially the same as the width and length of magnet surface 14, the shoe having concentric concave and convex surfaces with the convex surface being complementary to surface 14. The edges 18 of shoes 17 are beveled as shown in the figures, the bevel being in an inward direction from the convex surface to the concave surface.

An annular casting of nonmagnetic material generally indicated at 19 holds magnets 13 and shoes 14 together. Cast ring 19 is somewhat wider than magnets 13, as seen in FIGURE 2. The outer convex surface 21 of ring 19 is on the same diameter as the convex surfaces 15 of magnets 13, that is, surfaces 15 and 21 are flush or contiguous. At the location of magnets 13, surface 21 is relatively narrow, as seen in FIGURE 2, whereas surface 21 is relatively wide between magnets 13, as seen in FIGURE 3.

The thickness of ring 19 in its final form is equal to the combined thicknesses of magnets 13 and shoes 17, as seen in FIGURE 2, and the width of ring 19 is somewhat greater than the width of magnets 13 and shoes 17. The ring is thus formed with portions 22 and 23 which engage the axially spaced end surfaces 24 and 25, respectively, of magnets 13 and the end bevel edges 18 of shoes 17, portions 22 and 23 of ring 19 holding shoes 17 against magnets 13. If ring 19 is fabricated in accordance with the method to be described below, portions 22 and 23 will be partially removed in the areas between magnets, as seen in FIGURE 3. The inner surfaces of portions 22 and 23 adjacent shoes 17 will be flush with the inner shoe surfaces, as will be noted in FIGURE 2. Portion 23 of ring 19 extends radially outwardly to surface 21, whereas portion 22 extends outwardly a lesser distance, terminating in an inclined or fr ustoconical surface 26. The axially spaced outer surfaces of ring portions 22 and 23 are parallel to magnet surfaces 24 and 25.

FIGURES 4 and 5 illustrate a mold or die construction for forming assembly 19. The mold or die assembly is generally indicated at 27 and comprises a lower die member 28, an upper die member 29 and an intermediate die member 31. These die members are suitably fabricated of magnetic material such as steel and are of circular shape, member 28 having an upwardly facing flat central surface 32, a fiat surface 33 outwardly of surface 32 and spaced thereabove, and an outer retaining shoulder 34 for intermediate die member 31. Surfaces 32 and 33 are connected by an inclined or fr ustoconical surface 35 which serves to form ring surface 26. A plurality of circumferentially spaced magnet and shoe supporting elements 36 extending upwardly from surface 32 immediately inwardly of surface 35. Each element 36 comprises a fiat-topped projection extending upwardly somewhat higher than the level of surface 33 but with a pair of end surfaces 37 which are flush or contiguous with surface 33 as seen in FIGURE 5, thus forming vertical shoulders 38. The spacing between shoulders 38 of adjacent elements 36 is equal to the length of each magnet 13 in a circumferential direction so that a magnet 13 and a shoe 17 may be retained between each adjacent pair of elements 36, as seen in phantom lines in FIGURE 5.

Upper die member 29 has an inner downwardly facing flat annular surface 39 which terminates at a shoulder 41 having the same diameter as shoulder 34. A downward extension 42 is centrally formed within surface 39, this extension terminating in a lower flat surface 43 engageable with surface 32. The total length of extension 42 is such that the distance between surfaces 32 and 39 will be equal to the desired initial thickness of ring 19; this will be determined by the width of magnets 13 and shoes 17 in an axial direction. A plurality of circumferentially spaced downward projections 44 are provided on surface 39; these projections are shaped similarly to projections 36 so as to be in supporting relation with magnets 13 and shoes 17.

Intermediate die member 31 is of annular shape, having a lower flat surface 45 engagea-ble with surface 33 of die member 28 and an upper flat surface 46 engageable with surface 39 of die member 29. The distance between surfaces 45 and 46 will likewise be determined by the width of magnets 13 and shoes 17. Outer surface 47 of die member 31 is substantially the same as the diameter of shoulders 34 and 41, and the thickness of die member 31 is such that its inner surface 48 will be in supporting relation with the outer surfaces of magnets 13. A plurality of recesses 49 and 51 may be provided in die members 28 and 29, respectively, for separating purposes. It should be noted that the cylindrical surface 52 of extension 42 is spaced inwardly from surafce 48 a distance such that a space will exist between the concave surfaces of shoes 17 and die surface 52.

In carrying out the novel process of fabricating assembly 11, central die member 31 will be mounted on lower die member 28 and magnets 13 in their magnetized condition, together with shoes 17, will be placed with proper polar orientation between shoulders 38 on lower die member 28, the magnets resting on surfaces 37 of projections 36 and die surface 33, shoes 17 being supported by surfaces 37. Because of the magnetized condition of magnets 13, their outer convex surfaces will be held firmly against intermediate die member 31, and their inner concave surfaces will hold shoes 17. Glue or other adhesive material may be used between magnets 13 and shoes 17 for aiding in retention of the shoes on the magnets. Upper die member 29 will then be mounted on intermediate die member 31, projections 44 engagingthe upper portions of magnets 13 and shoes 17 while surface 43 of upper die member 29 engages surface 32 of lower die member 28. r

The molten material which will form ring 19 is then poured or injected into the cavity formed by the die members through a suitable gate (not shown). This material may be aluminum, zinc, bismuth or another nonmagnetic metallic or plastic substance having the desired strength characteristics. Heat from the material forced into the mold will at least partially demagnetize magnets 31, thus facilitating removal of assembly 11 from mold 27.

The gate and the sprue formed between surfaces 32 and 43 will then be removed, the sprue being indicated in dot-dash lines at 53 in FIGURE 2. Magnets 13 will then be demagnetized, this being done to facilitate the later machining step.

Assembly 11 may then be mounted in supporting ring 12. The ring is shown in FIGURE 2 as having an annular surface 54 for supporting assembly 11, this surface terminating in an inwardly extending shoulder 55. Ring 12 may be previously heated and assembly 11 slipped into the ring, portion 22 first, until it engages shoulder 55; an

appropriate lubricating substance may be used for this purpose if desired. As ring 12 cools, it will shrink into tight engagement with assembly 11, being in direct contact with exposed convex surfaces 15 of magnets 13 to form an efficient flux path.

The assembly comprising unit 11 and ring 12 may then be machined at room temperature to remove the excess portions of casting 19. These excess portions are indicated in dot-dash lines at 56 in FIGURES 2 and 3 and will comprise the material radially inwardly of inner shoe surfaces 17 and axially outwardly of the end surface 57 of supporting ring 12. Magnets 13 may then be remagnetized to complete the fabrication process.

FIGURES 7 and 8 show a slightly modified form of the magnet shoe, the shoe being indicated generally at 101. Shoe 161 is generally similar to shoe 17, having convex and concave surfaces with the convex surface complementary to the concave surface of magnet 102. However, the outer dimensions of shoe 131 are slightly larger than those of magnet 102, so that portions 193 of beveled edge 104 may be formed into coined or lanced retention lugs for aiding in the positioning and retention of the shoes on the magnets. Four such portions 103 are shown, one being located at the central portion of each beveled edge. The use of these lugs may eliminate the need for glue or other adhesive substance during the assembly process, and portions N3 will also coact with the cast material to enhance the rigidity of the assembly.

While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. In a method for fabricating a portion of a permanent magnet alternator of the type having a plurality of circumferentially spaced arcuate magnets with inwardly facing arcuate shoes and a supporting ring of magnetic material surrounding said magnet, the steps of placing said magnets and shoes in their proper circumferentially spaced relation but separate from said magnetic supporting ring, casting a continuous ring which engages the opposite axially spaced ends of said magnets and shoes and holds the shoes to the magnets as well as the shoes and their magnets in their proper circumferentially spaced relation, said cast ring having an excess portion extending radially inwardly of said inwardly facing shoe surfaces, the outwardly facing magnet surfaces being exposed at the outer cast ring diameter, demagnetizing said magnets, heating said supporting ring, slipping the unit consisting of the demagnetized magnets, shoes and cast ring into said heated supporting ring, permitting said supporting ring to cool so as to shrink into tight engagement with said unit and into direct contact with the exposed outwardly facing surfaces of said magnets to form an efficient flux path, machining the assembly comprising said unit and supporting ring at room temperature to remove said excess portions of the cast ring, to expose said inwardly facing shoe surfaces, and remagnetizing said magnets.

2. In a method for fabricating a portion of a permanent magnet generator of the type having a plurality of circumferentially spaced magnet bodies with radially facing shoes and a supporting ring of magnetic material and circumferentially surrounding said magnet bodies with said supporting ring being a pre-existing component normally serving a first function in a machine assembly other than a function as a portion of a generator and in such first function being adapted to be rotated, comprising the steps of placing said magnet bodies while magnetized and shoes in their proper circumferentially spaced relation but separate from said supporting ring, forming a unit separate from said supporting ring and having circumferential cluster of magnet bodies and shoes by casting a continuous ring of non-magnetic material which engages the opposite axially spaced ends of said magnet bodies and shoes and holds the shoes to the magnet bodies as Well as the shoes and magnet bodies in their proper circumferentially spaced relation with said magnet bodies held in said unit and being magnetically connected solely by high reluctance paths generally of non-magnetic material, and securing the separate unit consisting of the magnet bodies, shoes and cast ring to said supporting ringof the machine assembly with said magnet bodies opposite from the sides of the shoes substantially in contact with said supporting ring whereby a magnetic return path of loW reluctance is provided between associated magnet bodies, demagnetizing said bodies and said shoes prior to machining the separate unit, machining the unit with the magnet bodies unmagnetized and magnetizing the magnet bodies after machining, the magnet bodies being constructed of a ceramic material resulting in a ceramic magnet upon magnetization, the cast ring being made of a non-magnetic material and the supporting ring and shoes being made of a magnetic material.

References Cited UNITED STATES PATENTS Merrill 310-154 Armstrong et al. 310-153 Phelon 310-153 Raleigh 310-153 Mennesson 310-153 Anderson 29155.53 Blackburn 29-155.53 Strong 310-153 Blackburn 29-447 X Applegate 29-155.53 Cobb 29155.5

FOREIGN PATENTS JOHN F. CAMPBELL, Primary Examiner.

R. W. CHURCH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,368,275 February 13, 1968 Richard F. Eberline et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 56, for "surafce" read surface column 6, line l0,or "Strong" read Strang same column 6, after line 14, insert the following 2,963,599 12/1960 Gaylor Signed and sealed this 15th day of April 1969.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

2. IN A METHOD FOR FABRICATING A PORTION OF A PERMANENT MAGNET GENERATOR OF THE TYPE HAVING A PLURALITY OF CIRCUMFERENTIALLY SPACED MAGNET BODIES WITH RADIALLY FACING SHOES AND A SUPPORTING RING OF MAGNET MATERIAL AND CIRCUMFERENTIALLY SURROUDING SAID MAGNET BODIES WITH SAID SUPPORTING RING BEING A PRE-EXISTING COMPONENT NORMALLY SERVING A FIRST FUNCTION IN A MACHINE ASSEMBLY OTHER THAN A FUNCTION AS A PORTION OF A GENERATOR AND IN SUCH FIRST FUNCTION BEING ADAPTED TO BE ROTATED, COMPRISING THE STEPS OF PLACING SAID MAGNET BODIES WHILE MAGNETIZED AND SHOES IN THEIR PROPER CIRCUMFERENTIALLY SPACED RELATION BUT SEPARATE FROM SAID SUPPORTING RING, FORMING A UNIT SEPARATE FROM SAID SUPPORTING RING AND HAVING CIRCUMFERENTIAL CLUSTER OF MAGNET BODIES AND SHOES BY CASTING A CONTINUOUS RING OF NON-MAGNETIC MATERIAL WHICH ENGAGES THE OPPOSITE AXIALLY SPACED ENDS OF SAID MAGNET BODIES AND SHOES AND HOLDS THE SHOES TO THE MAGNET BODIES AS WELL AS THE THE SHOES AND MAGNET BODIES IN THEIR PROPER CIRCUMFERENTIALLY SPACED RELATION WITH SAID MAGNET BODIES HELD IN SAID UNIT AND BEING MAGNETICALLY CONNECTED SOLELY BY HIGH RELUCTANCE PATHS GENERALLY OF NON-MAGNETIC MATERIALL, AND SECURING THE SEPARATE UNIT CONSISTING OF THE MAGNET BODIES, SHOES AND CAST RING TO SAID SUPPORTING RING OF THE MACHINE ASSEMBLY WITH SAID MAGNET BODIES OPPOSITE FROM THE SIDES OF THE SHOES SUBSTANTIALLY IN CONTACT WITH SAID SUPPORTING RING WHEREBY A MAGNETIC RETURN PATH OF LOW RELUCTANCE IS PROVIDED BETWEEN AND SAID SHOES MAGNET BODIES, DEMAGNETIZING SAID BODIES AND SAID SHOES PRIOR TO MACHINING THE SEPARATE UNIT, MACHINING THE UNIT WITH THE MAGNET BODIES UNMAGNETIZED AND MAGNETIZING THE MAGNET BODIES AFTER MACHINING, THE MAGNET BODIES BEING CONSTRUCTED OF A CERAMIC MATERIAL RESULTING IN A CERAMIC MAGNET UPON MAGNETIZATION, THE CAST RING BEING MADE OF A NON-MAGNETIC MATERIAL AND THE SUPPORTING RING AND SHOES BEING MADE OF A MAGNETIC MATERIAL. 